Abnormal Meiosis

Factors such as meiotic errors, disease, environmental factors can interfere with meiosis and contribute to genetic disorders. On rare occasions, chromosomes may be gained or lost from cells. This is called non-disjunction.

NON-DISJUNCTION The failure of homolgous chromosomes to move to opposite poles of the cell during meiosis. This results in an abnormal number of chromosomes in the daughter cells

NON-DISJUNCTION In humans, this can result in 22 or 24 chromosomes When a gamete with an abnormal number of chromosomes joins with a normal number, it can result in monosomy or trisomy.

NON-DISJUNCTION (Trisomy) A chromosomal abnormality where there are 3 homologous chromosomes in place of a homologous pair. If a gamete with 24 chromosomes joins with a normal gamete (having 23 chromosomes) from the opposite sex, the resulting zygote will have 47 chromosomes instead of 46 (the normal chromosome number). The zygote will have 22 pairs of chromosomes and three copies of one chromosome

NON-DISJUNCTION (Monosomy) A chromosomal abnormality in which there is a single chromosome in place of a homologous pair If a gamete with 22 chromosomes joins with a normal gamete (having 23 chromosomes) from the opposite sex, the resulting zygote will have 45 chromosomes. Although the zygote will have 22 pairs of chromosomes, it will be missing one of its homologous chromosomes for the remaining pair.

Diagnosing Non-Disjunction Non-disjunction disorders are usually confirmed by preparing a karyotype. Technicians usually prepare a karyotype by obtaining and mixing a small sample of white blood cells with a solution that stimulates mitotic division. A different solution is added that stops division at metaphase, when the chromosomes are most condensed and can be photographed and sorted.

Diagnosing – Prenatal Testing This is testing for a genetic disorder before birth, usually for females over 35 There are a number of ways to do this: CVS (chorionic villus sampling) happens at 8 weeks Amniocentesis (collecting fluid from the sac) using a syringe and ultrasound Women can get their blood tested called multiple marker testing (tests for hormone levels)at 15 and 20 weeks

Assisted Reproductive Technologies In Vitro Fertilization (IVF) Fertilization outside of the body Artificial Insemination (intrauterine insemination) Placement of sperm into the reproductive tract of the female